Unfortunately, SOHO Business Cards does not directly integrate with Aperture. It only integrates with iPhoto. This isn't because we don't want to support Aperture. Rather, Apple hasn't made any public API's available to developers for accessing Aperture photos. We've researched this extensively and discovered a few developers with solutions that access the Aperture database using non-public methods, but we've decided not to take this course since Apple could break this access at any time leaving customers upset and blaming us. We're still hoping Apple makes a public solution for developers:)
That said, you can drag and drop photos from the Aperture application to your design in SOHO Business Cards. It's just that your Aperture photos won't show up in SOHO Business Cards' built-in photo browser.